• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.1 s.12
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• pp.15-24
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• 2004

Generally, a ${\pi}$-type girder composed of two I-type girders is known to have a significant disadvantage in wind resistance design because of aerodynamic instability. A representative bridge for this girder was Tacoma Narrows Bridge. Since Tacoma Narrows Bridge had very low stiffness of the bridge structure and its cross-section shape had aerodynamic instability, the bridge collapsed after severe torsion and vibration events in 19m/s wind speed. Aerodynamic vibration can be avoided by enhancing structural stiffness and damping factor and conducting a study of cross-section shapes. This study shows the angle of attack for the four-span cable stayed bridge having ${\pi}$-type cross-section and describes the aerodynamic characteristics of the changed cross-section with aerodynamic vibration damping additions, by carrying out two-dimension vibration tests. As a result of uniform flow and turbulent flow, the study shows that because the basic ${\pi}$-type cross-section alone can have efficient wind resistant stability, there is no need to have additional aerodynamic damping equipment. Since this four 230m-main-span bridge has a large frequency and also has a big stiffness compared to other bridges containing a similar cross-section, it has aerodynamic stability under the design wind speed.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.1
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• pp.3-8
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• 2000

This paper describes a development of self tuning scheme for PI and PO type fuzzy controllers. The output scaling factor(SF) is adjusted on-line by fuzzy rules according to the current trend of the controlled process. The rule-base for tuning the output SF is defined on error and change of error for the controlled variable using the most natural and unbiased membership functions. Simulation results demonstrate the better control performance can be achieved in comparison with Ziegler-Nichols(Z-N) PID controllers.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.387-390
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• 1996

In this paper, A new PI-type reaching law for variable structure control is proposed to alleviate the chattering and improve the robustness properties in the presence of matched uncertainty. The proposed reaching law consists of a proportional term and an integral term. And the dynamics of switching function can easily be specified by using the second-order system analysis method. And also the proposed scheme has the advantages of alleviating the chattering than Gao's one and reducing the influence of uncertainties by band pass filter characteristic. The efficiency of the proposed method has been demonstrated by simulations for Dutch Roll damping in a light aircraft.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.3
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• pp.214-218
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• 1997

We propose a VSC(Variable Structure Controller) with a PI-type reaching law. In General, conventional VSCs with a reaching law including a discontinuous term have the chattering problem, and thus the system may be unstable due to the disregarded high frequency dynamics in the modeling process. To resolve this problem, the PI-type reaching law is proposed in this paper. The proposed reaching law makes it easy to determine the reaching dynamics as well as the reaching time by utilizing the 2nd-order system analysis. Furthermore, since the discontinous term is not involved in the reaching law, the chattering is considerably reduced. To show the effectiveness of the proposed scheme, the stability of the proposed system is proved by Lyapunov method and the computer simulations are performed for the Ball Balance System.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.1
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• pp.1-6
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• 2015

Generating output characteristics of a ${\pi}$-type piezoelectric harvester depending on size of the ceramic and the elastic body were studied. The ${\pi}$-type piezoelectric harvester consists of a rectangular piezoelectric ceramic and a ${\pi}$ shaped elastic body. If the tensions is applied at both ends of an elastic body legs, the piezoelectric effect occurs at the ceramics through the form change of the elastic body. The structure of this ${\pi}$-type harvester can be used in a various area than an existing type generator, because it prevent from direct pressure to the ceramic. Generating characteristics of the harvester were analyzed by using finite element method program. The piezoelectric harvester was fabricated on the basis of analyzed results and attached on a frequency controllable vibrator to measure the output characteristics. And generating characteristics were defined by comparing analysis results and experimental results. The highest output voltage was obtained when the ceramic length, thickness were 20 mm, 0.5 mm in the analysis result. And experiment was performed by analysis results at low frequency region, output voltage was generated about 6 V.

• Proceedings of the KIEE Conference
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• 1997.07f
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• pp.2062-2065
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• 1997

컨버터나 인버터의 운전에 있어서 비간섭 전류제어는 그 시스템의 성능에 직접적으로 영향을 주는 중요한 요인이다. 하지만 일반적인 비간섭 제어방식은 모터나 입력 인덕터에 파리미터 오차가 있으면 잘 동작하지 않는다 이 논문에서는 PI 형태의 새로운 비간섭제어 방식을 제안하였다. 이 방식의 가장 큰 장점은 파라미터 오차에 대해 강인성을 가지는 것이다. 시뮬레이션을 통하여 제안된 제어기의 성능을 살펴보았다.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1815-1817
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• 1999

In this paper, the generation of high pretilt angle in nematic liquid crystal (NLC) by dipping effect on three kinds of the rubbed polyimide (PI) surface was investigated. The generated pretilt angle of NLC increases due to dipping effect before rubbing treatment on two kinds of the rubbed PI surface with side chain. The generated pretit angle in NLC by using dipping effect after rubbing treatment on PI surface with short side chain is high compared to the PI surface with long side chain. The generated pretit angle of the positive type NLC $(\Delta{\varepsilon}>0)$ is higher as than that of the negative type NLC $({\Delta}{\varepsilon}<0)$ by using dipping effect before rubbing treatment on homeotropic layer. The generated pretilt angle of NLC is attributed to perpendicular component of permittivity ${\varepsilon}_{\perp}$ of NLC on rubbed PI surface.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.113-116
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• 2006

In this paper, the fairing effects on the aerodynamics stability of basic plate-girder sections are investigated trough wind tunnel tests. As basis sections, two types of $\pi$-type shape sections with aspect ratios(D/B) of 1/5 and 1/10 are employed as the basic sections. And three types of triangular fairings are applied such as right-angled triangle(F1), inverted right-angled triangle(F2) and regular triangle(F3). The effects of attack angle on the dynamic response of each section are also investigated. As the results of experiments, fairings F2 is most effective to suppress flutter phenomenon or vortex induced vibration among three types of fairings.

• Journal of Advanced Navigation Technology
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• v.9 no.1
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• pp.34-40
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• 2005

In this paper we propose a turbojet engine controller of unmanned aircraft based on the Fuzzy-PI algorithm. To prevent any surge or a flame out event during the engine acceleration or deceleration, the PI-type fuzzy controller effectively controls the fuel flow input of the control system. The fuzzy inference rule made by the logarithm function of acceleration error improves the tracking error. Computer simulations applied to the linear model of a turbojet engine show that the proposed method has good tracking performance for the reference acceleration and deceleration commands.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.6
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• pp.661-667
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• 2004

The control of tilt angle for nematic liquid crystal (NLC) with negative and positive dielectric anisotropy on the rubbed homeotropic polyimide (PI) using baking method by hot plate equipment was investigated. LC tilt angle decreased with increasing baking temperature and time. Especially, the low LC tilt angle of positive type NLC (Δ$\varepsilon$＞0) on the rubbed homeotropic PI surface by increasing temperature and time was measured. The tilt angle of positive type NLC(Δ$\varepsilon$＞0) is smaller than that of the negative type (Δ$\varepsilon$＞0) on rubbed PI with increasing baking temperature and time. We consider that the tilt angle of NLC is decreased due to increasing the steric interaction between horizon component of permittivity $\varepsilon$ = of NLC and the stress of polymer side chain by high temperature. As the increase of baking temperature, we obtain that AFM (atomic force microscope) image of rubbed PI surface using Hot-plate method has formed better solid micro-groove structure than oven method.